1. Field of the Invention
The present invention relates to a control apparatus to identify an error occurring at a fuel system of an internal combustion engine that includes a fuel injection mechanism (in-cylinder injector) injecting fuel at high pressure into a cylinder and a fuel injection mechanism (intake manifold injector) injecting fuel towards an intake manifold or intake port. Particularly, the present invention relates to a control apparatus properly identifying an error at a high-pressure fuel system.
2. Description of the Background Art
There is known an engine including a first fuel injection valve (in-cylinder injector) for injecting fuel into the combustion chamber of a gasoline engine and a second fuel injection valve (intake manifold injector) for injecting fuel into an intake manifold or intake port, wherein the in-cylinder injector and the intake manifold injector partake in fuel injection according to the engine speed and load of the internal combustion engine. There is also known a direct injection engine including only a fuel injection valve (in-cylinder injector) to inject fuel into the combustion chamber of the gasoline engine. In a high-pressure fuel system including an in-cylinder injector, fuel having pressure increased by a high-pressure fuel pump is supplied to the in-cylinder injector via a delivery pipe, whereby the in-cylinder injector injects high-pressure fuel into the combustion chamber of each cylinder in the internal combustion engine.
Further, there is also known a diesel engine with a common rail type fuel injection system. In the common rail type fuel injection system, fuel having pressure increased by a high-pressure fuel pump is stored at the common rail. High-pressure fuel is injected into the combustion chamber of each cylinder in the diesel engine from the common rail by opening/closing an electromagnetic valve.
For the purpose of setting the fuel at high pressure in the internal combustion engine, a high-pressure fuel pump that drives a cylinder through a cam provided at a drive shaft coupled to a crankshaft of the internal combustion engine is employed.
Japanese Patent Laying-Open No. 10-176592 discloses a fuel pressure diagnostic device of a fuel injection device for an internal combustion engine that can diagnose the presence of an error in the fuel pressure at high accuracy. This fuel pressure diagnostic device includes a fuel delivery unit delivering fuel to be supplied to each cylinder of the internal combustion engine, a storage unit storing fuel delivered from the fuel delivery unit, a fuel injection mechanism provided for each cylinder to inject intermittently the fuel stored in the storage unit to the internal combustion engine, a fuel pressure sensor sensing the pressure of the fuel stored in the storage unit, a fuel control unit controlling the pressure of fuel stored in the storage unit by controlling the fuel delivery unit based on the fuel pressure sensed by the fuel pressure sensor, and a pressure abnormality diagnostic unit diagnosing whether there is an abnormality in the fuel pressure under control of the pressure control unit. The pressure abnormality diagnostic unit diagnoses whether there is an abnormality in the fuel pressure when each fuel injection mechanism is inactive.
In accordance with the fuel pressure diagnostic device disclosed in the aforementioned publication, fuel that is to be delivered to each cylinder of the internal combustion engine by the fuel delivery unit is stored in the storage unit. The fuel stored in the storage unit is injected intermittently into each cylinder by the fuel injection mechanism provided at each cylinder. The pressure of fuel stored in the storage unit is sensed by the fuel pressure sensor. Based on the sensed fuel pressure, the fuel delivery unit is controlled through the pressure control unit. The fuel pressure under control of the pressure control unit is diagnosed by the pressure abnormality diagnostic unit when each fuel injection mechanism is inactive. As a result, the presence of an error in the pressure fuel is diagnosed based on fuel pressure immune to pressure variation by the intermittent fuel injection. In an active state where each fuel injection mechanism injects fuel intermittently, the pressure of fuel stored in the storage unit will vary in a certain range. Since it is difficult to sense the pressure of fuel actually controlled, leakage of fuel caused by malfunction or the like of the fuel injection mechanism cannot be readily detected. Abnormality diagnosis of fuel pressure is conducted when the fuel injection mechanism is inactive. Therefore, a fuel pressure error can be identified based on fuel pressure that will not vary in accordance with the intermittent injection.
In the above-described internal combustion engine that includes an in-cylinder injector injecting fuel at high pressure towards a cylinder and an intake manifold injector that injects fuel towards the intake manifold or intake port, it is to be noted that the in-cylinder injector and the intake manifold injector partake in fuel injection according to the performance required of the internal combustion engine. When fuel homogeneity, for example, is required, fuel will be injected from only the intake manifold injector. Even in such a case where fuel is to be injected from only the intake manifold injector, the pressure of fuel is raised to approximately 8-13 MPa by a high-pressure pump in the high-pressure fuel system that supplies high-pressure fuel to the in-cylinder injector so that fuel (although not injected at that time from the in-cylinder injector) can be injected immediately from the in-cylinder injector in response to a subsequent instruction from the control device. This high-pressure fuel that is not injected (not consumed) will be increased in temperature by the heat received from the internal combustion engine. Accordingly, the fuel pressure is apt to increase. If detection is made of an abnormality in the high-pressure fuel system based on the aforementioned excessive increase of the fuel pressure in such a case, erroneous determination will be made even though the high-pressure fuel system per se is proper. The fuel pressure diagnostic device disclosed in Japanese Patent Laying-Open No. 10-176592 merely teaches abnormality diagnosis of fuel pressure when the fuel injection mechanism is inactive. It is not applicable to the case where an internal combustion engine including an in-cylinder injector and an intake manifold injector is operated with fuel injected from the intake manifold injector (low pressure side) and not from the in-cylinder injector (high pressure side).